Comparison of survival and embryonic development in human oocytes cryopreserved by slow-freezing and vitrification.
OBJECTIVE
To compare the survival, fertilization, early embryonic development, and meiotic spindle assembly and chromosome alignment in frozen-thawed human oocytes after slow-freezing and vitrification.


METHODS
A randomized study.


METHODS
A university-affiliated assisted reproductive center.


METHODS
Donated extra eggs from women undergoing assisted reproduction treatment.


METHODS
A total of 605 mature oocytes were divided into a slow-freezing group and a vitrification group for cryopreservation.


METHODS
After frozen-thawing, the oocyte survival rate, spindle assembly, and chromosome alignment were compared. The surviving oocytes were inseminated by intracytoplasmic sperm injection, and the rate of fertilization and embryo development were also compared in two groups.


RESULTS
The oocyte survival rate was statistically significantly lower in the slow-freezing group (75 out of 123, 61.0%) than the vitrification group (268 out of 292, 91.8%). The fertilization rate was the same for both groups, but the cleavage rate of zygotes was statistically significantly different between two groups: (slow-freezing, 25/46 (54.4%) versus vitrification, 142 out of 182 (78.0%). There was a considerable difference in the percentage of high-quality embryos between slow-freezing and vitrification groups: 6 out of 25 (24.0%) versus 60 out of 142 (42.3%), respectively. The percentage of blastocyst development was statistically significantly higher in the vitrification group (47 out of 60, 33.1%) than in the slow-freezing group (3 out of 25, 12.0%). There was a much higher percentage of oocyte abnormalities in terms of spindle assembly and chromosome alignment in the slow-freezing group (25 out of 64, 39.1%) compared with the vitrification group (11 out of 62, 17.7%).


CONCLUSIONS
Vitrification is superior to the slow-freezing method, leading to improved oocyte survival rate, fertilization, and embryonic development in vitro. These results may be related to vitrified human oocytes incurring less damage to spindle integrity and chromosome alignment.
Cao
Yun-Xia
YX
Center for Reproductive Medicine, Department of Obstetrics and Gynecology, The First Affiliated Hospital of Anhui Medical University, Hefei, People's Republic of China. Electronic address: caoyunxia6@126.com.
Xing
Qiong
Q
Center for Reproductive Medicine, Department of Obstetrics and Gynecology, The First Affiliated Hospital of Anhui Medical University, Hefei, People's Republic of China.
Li
Li
L
Center for Reproductive Medicine, Department of Obstetrics and Gynecology, The First Affiliated Hospital of Anhui Medical University, Hefei, People's Republic of China.
Cong
Lin
L
Center for Reproductive Medicine, Department of Obstetrics and Gynecology, The First Affiliated Hospital of Anhui Medical University, Hefei, People's Republic of China.
Zhang
Zhi-Guo
ZG
Center for Reproductive Medicine, Department of Obstetrics and Gynecology, The First Affiliated Hospital of Anhui Medical University, Hefei, People's Republic of China.
Wei
Zhao-Lian
ZL
Center for Reproductive Medicine, Department of Obstetrics and Gynecology, The First Affiliated Hospital of Anhui Medical University, Hefei, People's Republic of China.
Zhou
Ping
P
Center for Reproductive Medicine, Department of Obstetrics and Gynecology, The First Affiliated Hospital of Anhui Medical University, Hefei, People's Republic of China.
D001755:Blastocyst / Q000166:cytology / Q000378:metabolism / Q000502:physiology / Q000648:ultrastructure; D002470:Cell Survival / Q000502:physiology; D002877:Chromosomes, Human / Q000378:metabolism; D015925:Cryopreservation / Q000379:methods*; D046149:Embryo Culture Techniques; D047108:Embryonic Development / Q000502:physiology*; D005260:Female; D005615:Freezing; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D009865:Oocytes; D011247:Pregnancy; D011897:Random Allocation; D020554:Sperm Injections, Intracytoplasmic; D008941:Spindle Apparatus / Q000502:physiology; D013997:Time Factors